Owing to development of the science and technology, liquid crystal displays (LCDs) have found wide application in people's daily life. Conventional edge-lit LCDs all require use of a light guide plate, and the light guide plate must be positioned onto a backplate. Generally, in conventional positioning practices, a tab or some other positioning structure is formed at a side edge of the light guide plate by use of a computerized numerical control (CNC) machine tool, and a positioning groove or a positioning post is formed in the backplate. Thus, the light guide plate and the backplate can be assembled together through engagement of the tab and the positioning groove or positioning post. However, this adds to the manufacturing complexity of the light guide plate and reduces the product yield of light guide plates.